The present invention describes herein relates to the field of measuring pressure changes in sealed systems. More specifically, the invention relates to measuring pressure changes in sealed lamps. The invention especially relates to measuring pressure changes due to leaks in sealed lamps used in an infrared jammer. The principles of the invention may also be applied to lamps used in spectroscopy.
Lamps used in infrared jamming and other applications contain evacuated or pressurized gases in a sealed chamber. Such lamps are surrounded by sealed envelopes. When leaks occur into the evacuated chamber, catastrophic lamp failure or implosion may occur resulting in injury to personnel and extensive property damage. Accordingly, it would be desirable to have a device which measures leakage into or out of a sealed envelop to determine the operational status of the lamp and to predict shelf and operating lifetimes without a resultant lamp failure. More specifically, a sealed lamp assembly may be comprised of an inner light source that is surrounded by an outer envelope. The space between the light source and the outer envelope may be evacuated. A device which measures leakage from the light source to the evacuated space defined by the light source and envelop (the enveloped space) would be desirable to determine the operational status of the light source and to predict shelf and operating lifetimes.
In a lamp assembly having an inner light source and an outer envelope, the outer envelope is not designed for a discharge in that there are no electrodes present in the outer envelope. Yet it would be desirable to measure leakage into the enveloped space without physically invading the enveloped space.
A sealed lamp may not have an outer envelope and an enveloped space, but may be a simple sealed bulb of some sort.
Standard prior art vacuum measurement devices such as McLeod, Pirani, thermocouple, or ionization gauges are not suitable for a pressure determination in such a sealed lamp because they would actively interfere or alter the sealed lamp system. No simple modification of such a sealed lamp is possible to accommodate the requirements of the prior art vacuum measurement systems which would require invasion into the sealed lamp. It would be desirable to be able to measure leakage into or out from a sealed lamp without invading the sealed lamp.
There is a phenomenon known as the optogalvanic effect. The optogalvanic effect was first reported by F. M. Penning in Physics, Vol. 8, page 137 (1928). In the optogalvanic effect, a gas is ionized; and, then, the steady-state-discharge is illuminated (probed) with ultraviolet-visible radiation. The change in the extent of ionization due to irradiation is monitored galvanically (by current flow) across the discharge. The galvanic signals (current flow) arise from optical absorption corresponding to nonionizing electronic transitions of the probed species.
The optogalvanic effect received little attention until the work of Green et al. discussed it in Appl. Phys. Lett., Vol. 29, page 5-747 (1976). Since that time, the optogalvanic effect has been used extensively (see Webster et al. Laser Focus, Vol. 19, page 41 (1983)) for high resolution atomic and molecular spectroscopy, laser stabilization and calibration, and chemical analysis. The method has been used successfully for studies involving hollow cathode DC discharges, RF discharges, plasmas, flames and explosions. The optogalvanic effect measurement is quite amenable to diverse irradiation conditions including pulsed, continuous wave, coherent, or broadband sources. Detection circuits are designed to correspond with both the pumping and probing devices.